IMAR, Department of Earth Sciences, University of Coimbra, 3000-272 Coimbra, Portugal.
J Environ Radioact. 2010 Oct;101(10):875-82. doi: 10.1016/j.jenvrad.2010.05.014. Epub 2010 Jun 15.
In order to evaluate the influence of faulting on the variability of geogenic radon at detailed scale (1:2000), data on gamma ray fluxes, U and Th concentrations in rocks, radon in soil-gas and radon in groundwater were collected in three target areas on the Oliveira do Hospital region (Central Portugal). This region stands on the Iberian Uranium Province, and is dominantly composed of Hercynian granites and metasedimentary rocks of pre-Ordovician age, crosscut by faults with dominant strike N35 degrees E, N55 degrees E and N75 degrees E. Radiometric anomalies are frequent, associated with faults of the referred systems and metasedimentary enclaves; the analytical data confirms that these anomalies are produced by local high uranium contents in rocks and fault-filling materials (n=34, range 13-724 ppm), while other radiogenic elements are relatively constant (e.g. Th 4-30 ppm). Radon concentration in soil can be extremely high, up to 12,850 kBq m(-3) (n=215), with a large proportion of results above 100 kBq m(-3). Unsurprisingly, groundwater also shows high radon concentrations, with observed values in the range 150-4850 Bq.L(-1) (n=17). From the results it is concluded that metasedimentary enclaves, as well as faults, can accumulate uranium from circulating fluids, and as a consequence, strongly locally enhance geogenic radon potential. Due to this fact, for the purpose of land use planning in such uranium-enriched regions, very detailed geological mapping is needed to precisely recognize radon high risk areas. A correlation between radon concentration in soil or in groundwater and gamma ray fluxes was established pointing to the possible use of these fluxes as a first step in assessing geogenic radon potential, at least to geological setting similar to the study area.
为了评估断裂对地质镭射气变化的影响，在葡萄牙中部奥利韦拉多霍坦地区的三个目标区域收集了伽马射线通量、岩石中的 U 和 Th 浓度、土壤气体中的镭射气和地下水中的镭射气数据。该地区位于伊比利亚铀矿区，主要由海西期花岗岩和前奥陶纪变质岩组成，被主导走向为 N35 度 E、N55 度 E 和 N75 度 E 的断层穿过。辐射异常频繁，与上述系统的断层和变质岩包体有关；分析数据证实，这些异常是由岩石和断层填充材料中局部高铀含量（n=34，范围为 13-724ppm）引起的，而其他放射性元素则相对稳定（例如 Th 为 4-30ppm）。土壤中的镭射气浓度可能非常高，高达 12,850kBq m(-3)（n=215），其中很大一部分结果高于 100kBq m(-3)。毫不奇怪，地下水中也显示出高浓度的镭射气，观测值范围为 150-4850Bq.L(-1)（n=17）。结果表明，变质岩包体和断层都可以从循环流体中积累铀，因此强烈地局部增强了地质镭射气的潜力。鉴于这一事实，为了在这些富铀地区进行土地利用规划，非常需要进行详细的地质测绘，以准确识别镭射气高风险区域。建立了土壤或地下水中的镭射气浓度与伽马射线通量之间的相关性，指出可以将这些通量用作评估地质镭射气潜力的第一步，至少对于与研究区域类似的地质背景而言是如此。
